A method for high-rate plasma etching of silicon is described, e.g., in published German patent document DE 42 41.045, etching being alternated with deposition of a Teflon-like polymer on the side walls of etched structures, which protects these walls from an etching operation during the subsequent etching steps. Gases which provide fluorine radicals in plasma, such as SF6, NF3, or ClF3, are used as the etching gases. Gases which provide Teflon-forming monomers in plasma, such as C4F8 or C3F6, are used as the passivation gases. This method allows etching rates of up to 20 μm/minute with excellent structure precision and selectivity even in regard to simple mask materials such as photoresist or SiO2.
In the method described in published German patent document DE 42 41 045, comparatively short deposition steps and/or passivation gas steps and longer lasting etching steps are used in order to achieve the highest possible etching rate. Formulas in which passivation gas steps of 3 to 5 seconds each and etching steps of 10 to 12 seconds each alternate with one another are typically used in connection with inductively coupled plasma sources. In the case of shorter passivation gas steps, it becomes increasingly more difficult to reproduce them with the required precision over a very large number of cycles.
An object of the present invention is to provide a plasma system and a method which make it possible to achieve a higher etching rate when anisotropically etching silicon as the substrate, in comparison to the prior art, while simultaneously providing greater profile control and also greater mask selectivity.